Material characteristics and building technique for the rammed earth wall of the 13th Korean fortress in Ganghwa

This study identifies the technique applied for building the rammed earth wall of the 13th Korean fortress, Ganghwa Jungseong, by analyzing its physical, mineralogical, granulometric, and geochemical characteristics. Furthermore, mutual homogeneities between the rammed earth wall and host rock, top soil, and sub-surface soil collected around the fortress were interpreted. The ground of the rammed earth wall was not created artificially but made via soil preparations containing loamy soils from weathered bedrock. The foundation part was built using various layers of soils having different colors, magnetic susceptibilities, particle sizes, and organic components. In particular, a layer of loamy saprolite was generated to enhance the stability of the foundation and improve ventilation and draining throughout the structure. The body of the wall is composed of silty loam at the bottom and silty loam to loam from the middle to the top. Techniques that alternately harden soils using different particle sizes enable external shock absorption and prevent crack formation owing to temperature changes during winter and summer. The rammed earth wall and the soils around the fortress contained related rock-forming materials had similar magnetic susceptibilities and geochemical characteristics, which indicated that they have a genetically common source. Moreover, the rammed earth wall was built using the soil weathered from the banded gneiss because it was correlated to the banded gneiss constituting the bedrock around the fortress.